M-Nitrobenzenesulphonic acid

The melting points of a number of sulphonacetamides are —benzene-sulphonic acid, 125° p-toluenesulphonic acid, 137° p-bromobenzene-sulphonic acid, 203° m-nitrobenzenesulphonic acid, 189° p-nitroben-zenesulphonic acid, 192° naphthalene-a-sulphonic acid, 185° and naphthalene-p-sulphonic acid, 146°. 

In a 500 ml. bolt-head flask, provided with a mechanical stirrer, place 70 ml. of oleum (20 per cent. SO3) and heat it in an oil bath to 70°. By means of a separatory funnel, supported so that the stem is just above the surface of the acid, introduce 41 g. (34 ml.) of nitrobenzene slowly and at such a rate that the temperature of the well-stirred mixture does not rise above 100-105°. When all the nitrobenzene has been introduced, continue the heating at 110-115° for 30 minutes. Remove a test portion and add it to the excess of water. If the odour of nitrobenzene is still apparent, add a further 10 ml. of fuming sulphuric acid, and heat at 110-115° for 15 minutes the reaction mixture should then be free from nitrobenzene. Allow the mixture to cool and pour it with good mechanical stirring on to 200 g. of finely-crushed ice contained in a beaker. AU the nitrobenzenesulphonic acid passes into solution if a little sulphone is present, remove this by filtration. Stir the solution mechanically and add 70 g. of sodium chloride in small portions the sodium salt of m-nitro-benzenesulphonic acid separates as a pasty mass. Continue the stirring for about 30 minutes, allow to stand overnight, filter and press the cake well. The latter will retain sufficient acid to render unnecessary the addition of acid in the subsequent reduction with iron. Spread upon filter paper to dry partially. 

Place 84 g. of iron filings and 340 ml. of water in a 1 - 5 or 2-litre bolt-head flask equipped with a mechanical stirrer. Heat the mixture to boiling, stir mechanically, and add the sodium m-nitrobenzenesulphonate in small portions during 1 hour. After each addition the mixture foams extensively a wet cloth should be applied to the neck of the flask if the mixture tends to froth over the sides. Replace from time to time the water which has evaporated so that the volume is approximately constant. When all the sodium salt has been introduced, boU the mixture for 20 minutes. Place a small drop of the suspension upon filter paper and observe the colour of the spot it should be a pale brown but not deep brown or deep yellow. If it is not appreciably coloured, add anhydrous sodium carbonate cautiously, stirring the mixture, until red litmus paper is turned blue and a test drop upon filter paper is not blackened by sodium sulphide solution. Filter at the pump and wash well with hot water. Concentrate the filtrate to about 200 ml., acidify with concentrated hydrochloric acid to Congo red, and allow to cool. Filter off the metanilic acid and dry upon filter paper. A further small quantity may be obtained by concentrating the mother liquid. The yield is 55 g. 

Sodium m-nitrobenzenesulphonate has been proposed as an oxidising agent for vat dyes. It is available as a proprietary product and is claimed to react with leuco compounds more quickly than does peroxide. The solubilised vat leuco esters are most commonly hydrolysed and reoxidised to the insoluble parent dye using sodium nitrite and sulphuric acid. Alternative oxidising agents for vat leuco esters include hydrogen peroxide and ammonium metavanadate (NH4VO3), persulphates and nitric acid [218]. 

Benzenesulfonic acid, 3-nitro-, sodium salt Benzene-sulfonic acid, m-nitro-, sodium salt EINECS 204-857-3 HSDB 5614 Ludigol Ludigol F,60 Nacan m-Nitrobenzenesulfonic acid sodium salt Nitrobenzen-m-sulfonan sodny Nitrol S NSC 9795 Sodium 3-nitrobenzenesulfonate Sodium 3-nitrobenzenesulphon-ate Tiskan. 

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